Modern wireless communications networks employ different access techniques when a first network component intends to access a second network component. As an example for such access techniques the so-called random access (RA) scheme can be mentioned. The name “random access” indicates that access requests are generated in a random manner from the point of view of a network component receiving the access requests.
An exemplary RA scheme is specified by the 3rd Generation Partnership Project (3GPP) in section 6 of the 3GPP document TS 25.214, Version 4.4.0 (2002-03) titled “Technical Specification Group Radio Access Network; Physical Layer Procedures (FDD); Release 4”. Another exemplary RA scheme has been defined by standardization bodies for the Global System of Mobile Communications (GSM).
In RA schemes there may arise the situation that several network components simultaneously try to access a specific further network component, i.e. that access requests of different network components “collide”. Such collisions are detrimental to the quality of service since they result in access delays, message losses, etc. Consequently, various techniques have been introduced to avoid or reduce the detrimental effects of collisions inherent in RA schemes.
For example it has been proposed to implement repetition schemes according to which a specific network component repeatedly transmits its access request. A second way of reducing collisions inherent in RA schemes is to group the network components into specific access classes. The definition of such access classes can prohibit whole populations of network components the transmission of access requests based on their membership to a specific access class. Furthermore, collisions may be avoided or reduced by differentiating between access requests of different network components. To that end each access request may comprise a particular identification code, also called “random discriminator” (GSM) or “signature” (3GPP), which allows a network component that receives two or more access requests simultanueously to discriminate between random access requests of different network components.
An exemplary scheme for random access signaling on the basis of orthogonal codes is described in Matthias Schulist, Georg Frank, “Link Level Performance Results for a WCDMA Random Access Scheme with Preamble Power Ramping and Fast Acquisition Indication”, Proc. of VTC'99.-Fall. According to this random access signaling scheme a network component requesting access to a network resource randomly selects an identification code out of a set of predefined orthogonal codes and modulates the selected identification code onto a preamble signal. This preamble signal constitutes an access request that is transmitted to a further network component controlling access to the network resource. This further network component analyzes the received preamble signal with respect to the identification code modulated thereon and broadcasts an access control signal. The access control signal carries the analyzed identification code together with an indicator which indicates whether or not the access request associated with the analyzed identification code is granted.
In conjunction with the code-based signaling scheme discussed above and other signaling schemes that are based on the transmission of orthogonal codes there arises the necessity to evaluate the code that has been modulated onto a received signal. During such an evaluation the fact may be exploited that the received code is orthogonal to one or more further codes. However, due to imperfections of the transmission channel the received and demodulated code has lost its orthogonality to a certain extent. This loss of orthogonality makes the evaluation of the received and demodulated code more difficult and gives rise to evaluation errors.
There is a need for an improved mechanism which renders the evaluation of an initially orthogonal code that has been transmitted over an imperfect channel more reliable. In particular, there is a need for a method, a computer program product and a device for implementing such an evaluation mechanism.